| By Mark Davis
- MeteorObs News
This
year, the Lyrid (LYR) meteor shower reaches maximum activity on April 22nd, near
new moon - so conditions are very favorable for a good display! The actual time
of maximum is 04h UT, Universal Time, on April 22nd. Universal Time is the time
at Greenwich, England, so don't forget to adjust this for where you live. For
North Americans, this means the night of April 21st, which is also a weekend night!
As noted in the
International Meteor Organization (IMO) Handbook, the Lyrids are debris from Comet
Thatcher, C/1861 G1. This comet was discovered by A.E. Thatcher of New York on
April 5th, 1861, and independently by Baeker of Nauen, Germany, with the unaided
eye. It later brightened to about magnitude 2.5, with a tail of about 1 degree
in length. It was determined that the orbit of the comet was elliptical, and that
the comet returns about every 415 years. The
Lyrid shower is the oldest meteor shower for which observations have been found.
It was seen in ancient China over 2000 years ago. According to the IMO Handbook,
the Lyrid meteoroid stream - the actual debris shed by the comet - is highly inclined
in its orbit, meaning that its path doesn't come anywhere near our solar system's
planets, and hence isn't disrupted by the planets' gravity. Because of this, although
the stream is very old, it acts younger than its age! For instance, it has a short
period of maximum activity, only hours long, and has higher density concentrations
of material - clumps of debris - which can cause interesting outbursts of activity.
This shower lasts
from about April 16th until April 25th. At the time of maximum activity, the Zenithal
Hourly Rate (ZHR), should be about 15 meteors per hour. This means that if you
are out under a dark country sky, with the radiant, the area in the sky where
the meteors seem to come from, directly overhead, then you should see - on the
average - about 15 meteors every hour with your unaided eye. However,
rates for this shower can be variable - up to 90 meteors per hour! You won't know
if you are in for a surprise this year unless you get outside and take a look!
On the 22nd,
the radiant will be at 271 degrees, ie RA 18h 4.2m, Dec +34, which is approximately
halfway between the bright star Vega in Lyra and the star mu Herculis. To see
where this is on a star map, go to our NAMN Map #3 under http://web.infoave.net/~meteorobs/charts.html.
The NAMN charts
will also give you a refresher course in the spring constellations - and some
'standard' stars to judge meteor brightness with. Meteor radiants do move across
the sky from night to night though! The motion is not very noticeable over a night
or two, but over the course of a week, a radiant is at quite a different place
in the sky. For those of you watching the Lyrids away from the maximum date of
April 22nd, look at the Lyrid radiant map on the IMO website, under the 2001 Meteor
Shower Calendar: http://www.imo.net/calendar/cal01.html#Lyrids.
These are average
velocity meteors, at about 49 km/sec, so will be easier to observe for beginning
observers. These meteors will also be easier to capture with your camera, as they
won't fly by your camera field quite so quickly. If you want to try some photos,
use fast film, a normal (not a telephoto) camera lens set at almost wide open,
and a cable release and tripod. A series of 10 to 15 minute photos might be appropriate
if your light pollution is not too bad. Meteor photography is a science itself,
but even for beginning observers, it is fun to try. If you want to read more about
how the experts do it, check out the IMO website at http://www.imo.net/photo/index.html.
If you are new
to meteor observing, and just want to go out and see a meteor shower - then get
out a lawnchair and a sleeping bag, and just enjoy yourself! However, if you would
like to try actually recording meteor data, that we can use for the study of meteors,
then check out our NAMN Observing Guide at : http://web.infoave.net/~meteorobs/guide.html.
2. Other April
Showers... The Virginids (VIR), the ecliptical activity, continue into April,
as the radiant moves along the path of the ecliptic in the sky, a little motion
each day. These are almost slow meteors at about 30 km/sec. ZHR rates will be
about 5 meteors per hour. By mid-April, on the 15th, the radiant will be at 205
degrees, ie RA 13h 40.2m, Dec -8, which is about 5 degrees up to the left of the
bright star Spica, in Virgo. The
pi Puppids (PPU) reach a maximum on April 23rd, right after the Lyrid maximum,
and can be seen from about the 15th to 28th. At maximum on the 23rd, the radiant
will be at 110 degrees, ie RA 7h 19.8m, Dec - -45, which is about 15 degrees due
south of the star eta Canis Majoris, the bottom left foot star of Canis Major.
These are nice slow meteors, with a velocity of about 18 km/sec. ZHR rates are
variable, and have reached as high as 40 meteors per hour on occasion. The pi
Puppids are debris from Comet 26P/Grigg-Skjellerup, discovered in 1902 by John
Grigg of Thames, New Zealand, and J.F. Skjellerup of Cape of Good Hope, South
Africa. The eta Aquarids (ETA) start to become active about April 19th, although
won't reach a maximum until May 5th. These are fast meteors, at about 66 km/sec.
Rates at maximum in early May should reach about 60 meteors per hour. Rates in
April will be much less. On April 20th, the radiant will be at 323 degrees, ie
RA 21h 31.8m, Dec -7, which is about 1 degree south of the star beta Aquarius,
the star called Sadalsuud. Eta Aquarids are debris from Halley's Comet. Lastly,
the Sagittarids (SAG) start to appear about April 15th, and will last till about
mid-July. This is actually a complex of radiants near the ecliptic, and is surmised
to be the debris from a number of unknown bodies. On April 20th, the radiant will
be at 227 degrees, ie RA 15h 7.8m, Dec -18, which is about 7 degrees due north
of the star sigma Libra, the variable star known as Brachium. These meteors are
verging on slow, with a velocity of about 30 km/sec. ZHR rates are about 5 meteors
per hour. Fireballs have been associated with this meteor shower complex. Some
useful star charts can be printed off from our NAMN website. These show the constellations,
the RA and Dec star coordinates, and the brightness of certain standard stars
to help you judge the magnitudes of the meteors you see. This set of 4 charts
is available at: http://web.infoave.net/~meteorobs/charts.html.
There are several
bright planets in the sky in April. Mars moves from Ophiuchus to Sagittarius in
the latter part of the month. On April 1st it is at magnitude -0.2, on April 11th
at magnitude -0.5, and by the 21st has brightened to -0.7. Note that the smaller
the number, the brighter the object! Jupiter and Saturn are getting lower in the
western sky, in Taurus. Jupiter is at magnitude -2.1 for most of the month, and
Saturn is at -0.2. For
more advanced reading, or to find out information on other types of meteor observing
- video, photographic, radio, etc. - check out the website of the IMO at http://www.imo.net.
Additional reading on more minor showers can be found on Gary Kronk's 'Comets
and Meteor Showers' website at http://comets.amsmeteors.org.
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